Metal oxides have been used as encapsulating materials and as matrices for various applications such as cosmetics, biomaterials, optics, laser, florescence, etc. using a variety of methods.
Shells consisting of hybrid inorganic-organic structures with bulk and surface properties that are compositionally controlled have been described in Hall, Simon, R., et al, Cocondensation of Organosilica Hybrid Shells on Nanoparticle, Templates: A Direct Synthetic Route to Functionalized Core—Shell Colloids, Langmuir, 16:1454-1456, 2000.
The formation of silica shells on core silver particles by a modified Stöber process is reported by Matijevi et al in Journal of Colloid and Interface Science, Volume 221, Issue 1, 1 Jan. 2000, Pages 133-136. They also report on the formation of spherical particles of Cu(II) basic carbonate coated with amorphous titania by hydrolysis of Ti(IV) butoxide in Colloids and Surfaces A: Physicochemical and Engineering Aspects, Volume 81, 13 Dec. 1993, Pages 153-159. In this report they show how the thickness of the shell could be varied by altering the experimental conditions. White pigments (whiteners) were prepared by coating monodispersed silica particles with titania. The hiding power of this powder was evaluated as a function of the particle diameter, the thickness of the titania shell, and the calcination temperature. Matijevi et al, Journal of Colloid and Interface Science, Volume 156, Issue 1, 1 Mar. 1993, Pages 56-65.
Colloidal boehmite (AlOOH) rods were used as cores for the preparation of rods with a silica shell as described in van Bruggen, M. P. B., Preparation and Properties of Colloidal Core—Shell Rods with Adjustable Aspect Ratios, Langmuir, 14:2245-2255, 1998.
A method for the encapsulation of fluorescent molecule into silica “nanobubbles” has been reported in Makarova, Olga V., et al., Adsorption and Encapsulation of Fluorescent Probes in Nanoparticles, J. Phys. Chem. B, 103:9080-9084, 1999. Bugnon, Philippe, (Bugnon, Philippe, Surface treatment of pigments. Treatment with inorganic materials, Progress in Organic Coatings 29: 39-43, 1996) has reported novel treatments of pigments with inorganic materials. Mikrajuddin, et al., (Mikrajuddin, et al, Stable photoluminescence of zinc oxide quantum dots in silica nanoparticles matrix prepared by the combined sol-gel and spray drying method, Journal of Applied Physics, 89:11, 2001) reported a ZnO/SiO2 nanocomposite with improved photoluminescence stability over ZnO colloids.
A spray drying approach has been used to apply 15-nm-thick SiO2 continuous coatings onto ZnS:Ag phosphor particles as described in Villalobos, Guillermo, R., et al., Protective Silica Coatings on Zinc-Sulfide-Based Phosphor Particles, J. Am. Ceram. Soc., 85(8):2128-2130, 2002.
Iskandar et al. have reported the preparation of microencapsulated powders by an aerosol spray method. The powders prepared by mixing two type of sols or sol-aqueous mixture precursor solution (Iskandar, Ferry, et al, Preparation of microencapsulated powders by an aerosol spray method and their optical properties, Advanced Powder Technol. 14(3):349-367, 2003). Iskandar et al. (Control of the morphology of nanostructured particles prepared by the spray drying of a nanoparticle sol. J Colloid Interface Sci., 265(2):296-303, 2003) additionally described the parameters influencing particles morphology by spray drying of silica nanoparticle sol.
Silica coating using layer by layer technique has been described in Dun, Huijuan, et al, Layer-by-Layer Self-Assembly of Multilayer Zirconia Nanoparticles on Silica Spheres for HPLC Packings, Anal, Chem., 76:5016-5023, 2004; Yuan, Junjie, et al., Organic Pigment Particles Coated with Colloidal Nano-Silica Particles via Layer-by-Layer Assembly, Chem. Mater., 17(4):3587-3594, 2005; Chung, Chau-Chyun, et al., Aqueous Synthesis of Y2O2S:Eu/Silica Core-Shell Particles, J. Am. Ceram. Soc., 88(5):1341-1344, 2005.
Y2O2:Eu red phosphor Powders coated with silica using sol-gel and heterocoagulation techniques were described in Jean, Jau-Ho, et al., Y2O2S:Eu Red Phosphor Powders Coated with Silica, J. Am. Ceram. Soc., 83(8):1928-1934, 2000.
Wilhelm, P., et al., (Wilhelm, P., et al, On-line tracking of the coating of nanoscaled silica with titania nanoparticles via zeta-potential measurements, Journal of Colloid and Interface Science, 293:88-92, 2006) reported nanoscaled spherical particles which were directly coated with titania nanoparticles by means of heterogenic coagulation.
The interaction between colloidal silica particles and the surface of ZnS-type phosphors has been studied in Merikhi, J., et al., Adhesion of Colloidal SiO2 Particles on ZnS-Type Phosphor Surfaces, Journal of Colloid and Interface Science, 228:121-126, 2000.
Sodium Silicate utilized to obtain a SiO2 coating on particles has been described in Wang, Hongzhi, et al., Effect of Polyelectrolyte Dispersants on the Preparation of Silica-Coated Zinc Oxide Particles in Aqueous Media, J. Am. Ceram. Soc., 85(8):1937-1940, 2002; U.S. Pat. No. 2,885,366; U.S. Pat. No. 3,826,670.
The sources of silica gels and factors controlling gel characteristics were described in Iler Ralph K., The Chemistry of Silica, Wiley-Interscience publication, 1979, pp. 510-533. U.S. Pat. No. 6,303,290 describes the encapsulation of biomaterials in porous glass-like matrices prepared via an aqueous colloidal sol-gel process. This process includes entrapment of the biomaterial in silica cages forms by controlling the gel characteristics.
JP02-002867 and JP 02-251240 disclose spherical particles made principally of silica, prepared by coprecipitation on of silica and UV filters such as benzophenone derivatives or dibenzoylmethane derivative, prepared in a water-in-oil emulsion.
U.S. Pat. No. 6,875,264 discloses a multilayer effect pigment including a transparent substrate, a layer of high refractive index material on the substrate, and alternating layers of low refractive index and high refractive index materials on the first layer. The high refractive index material may be titanium dioxide and the low refractive index material may be silicon dioxide.
U.S. Pat. No. 6,090,399 discloses a controlled release composition comprising one or more biologically active compounds incorporated into a metal oxide glass having a porous matrix.
U.S. Pat. No. 7,001,592 and U.S. Pat. No. 7,037,513 disclose a composition for topical application, e.g., a body-wash, where the additive contains a sol-gel encapsulated active either a sunscreen or a non-sunscreen. U.S. Pat. No. 7,052,913 discloses a biocompatible matrices, such as sol-gels encapsulating a reaction center, which may be administered to a subject for conversion of prodrugs into biologically active agents.
U.S. Pat. Nos. 6,303,149, 6,238,650, 6,468,509, 6,436,375, US2005037087, US2002064541, and International publication Nos. WO 00/09652, WO00/72806, WO 01/80823, WO 03/03497, WO 03/039510, WO00/71084, WO05/009604, and WO04/81222, disclose sol-gel microcapsules and methods for their preparation. EP 0 934 773 and U.S. Pat. No. 6,337,089 teach microcapsules containing core material and a capsule wall made of organopolysiloxane, and their production. EP 0 941 761 and U.S. Pat. No. 6,251,313 also teach the preparation of microcapsules having shell walls of organopolysiloxane. U.S. Pat. No. 4,931,362 describes a method of forming microcapsules or micromatrix bodies having an interior water-immiscible liquid phase containing an active, water-immiscible ingredient.
Another media, which can be utilized to protect sensitive ingredients, is doping within sol-gel matrices. In this method, monoliths, particles or other forms (such as thin films) are prepared, and the active ingredient is immobilized in the pores of the sol-gel matrix. The sol-gel matrix is doped with small amounts of the active ingredient. This method was utilized in WO98/31333, U.S. Pat. No. 6,495,352, and U.S. Pat. No. 5,292,801.
None of the prior art references teach or disclose a method for coating a solid, water insoluble particulate matter by a metal oxide layer with the ability to form and grow a coarse and dense layer on the surface of said particulate matter.
Thus there is a widely recognized need and will be highly advantageous to have a new process for metal oxide coating of a water insoluble particulate matter, enabling the growth of a metal oxide layer on said water insoluble particulate matter to the desired thickness. There is additionally a need for compositions especially for dermatological or agricultural use, characterized by the ability to isolate the active agent from the surrounding (by reducing its leaching through the metal oxide coating layer) thus lowering the side effects and toxicity associate with the active agent, and yet which are efficient at controlling the release of the active agent to the loci to be treated.